LED lighting device and illuminating device

ABSTRACT

According to one embodiment, an LED lighting device comprises at least one normally-on type switching element, an output generation unit that generates DC output by an on-off operation of the switching element, a semiconductor light emitting element that is lit by the DC output generated by the output generation unit, and a driving control unit that causes the switching element to perform an off operation using a current passed through the semiconductor light emitting element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/942,055filed Nov. 9, 2010. U.S. application Ser. No. 12/942,055 claims thebenefit of priority from Japanese Patent Applications No. 2009-256363,filed Nov. 9, 2009; No. 2010-027398, filed Feb. 10, 2010; No.2010-064436, filed Mar. 19, 2010; and No. 2010-234641, filed Oct. 19,2010. The entirety of all of the above-listed Applications areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to an LED lighting deviceand an illuminating apparatus provided with the LED lighting device.

BACKGROUND

Recently, a device in which an LED element is used as a light source isin practical use with improvement of optical performance of a LightEmitting Diode (LED) element. For example, a DC LED lighting device inwhich a switching means is utilized is widely used as an LED lightingdevice that lights the LED element.

Conventionally, for example, a transistor made of an Si (silicon)semiconductor is used as the switching means (switching element) of theLED lighting device. A transistor in which a wide-bandgap semiconductorsuch as SiC (silicon carbide), GaN (gallium nitride) and diamond is usedreceives attention.

Generally a wide-gap semiconductor has a normally-on characteristic inwhich a current is passed when a gate voltage is zero. Examples of thesemiconductor element in which the wide-gap semiconductor is usedinclude a JFET (Junction type FET), an SIT (Static InductionTransistor), an MESFET (Metal-Semiconductor FET:Metal-Semiconductor-Field-Effect-Transistor), an HFET (Hetero junctionField Effect Transistor), an HEMT (High Electron Mobility Transistor),and a storage type FET.

In order to securely turn off the semiconductor element (hereinafterreferred to as normally-on switch) having the normally-oncharacteristic, it is necessary for the LED lighting device to comprisea control circuit for negative gate voltage.

There is well known the fact that the LED lighting device having highcircuit efficiency is obtained by lighting the LED element with a DC-DCconverter. In the DC-DC converter, a switch element is driven using aninduced electromotive force, which allows constant current control to beperformed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of an illuminating apparatus according toan embodiment;

FIG. 2 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 3 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 4 illustrates a configuration example of a constant-voltage sourceaccording to an embodiment;

FIG. 5 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 6 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 7 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 8 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 9 illustrates an example of current and voltage waveforms in eachunit of an LED lighting device according to an embodiment;

FIG. 10 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 11 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 12 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 13 illustrates an example of current and voltage waveforms in eachunit of an LED lighting device according to an embodiment;

FIG. 14 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 15 illustrates a configuration example of an LED lighting deviceaccording to an embodiment;

FIG. 16 illustrates an example of an integrated circuit module of an LEDlighting device according to an embodiment; and

FIG. 17 illustrates an example of an integrated circuit module of an LEDlighting device according to an embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, an LED lighting devicecomprises at least one normally-on type switching element, an outputgeneration unit that generates DC output by an on-off operation of theswitching element, a semiconductor light emitting element that is lit bythe DC output generated by the output generation unit, and a drivingcontrol unit that causes the switching element to perform an offoperation using a current passed through the semiconductor lightemitting element.

Embodiments will be described below with reference to the drawings.

First Embodiment

FIG. 1 is a perspective view illustrating an illuminating apparatus towhich a power-supply device (LED lighting device) according to a firstembodiment is applied. The illuminating apparatus comprising thepower-supply device will briefly be described.

Referring to FIG. 1, an apparatus main body 1 comprises a disk-shapedbase 1 a. Ring LED illuminating lamps 2 and 3 having different diametersare concentrically disposed as a light source on the base 1 a. Acreamy-white shade 4 is mounted such that the LED illuminating lamps 2and 3 are covered therewith. A power-supply device 100 is disposed inthe apparatus main body 1. Although not illustrated, a reflective plate,a terminal, and wiring may be provided in the apparatus main body 1.

FIG. 2 illustrates a schematic configuration of the power-supply device100 that is incorporated in the apparatus main body 1 of theilluminating apparatus illustrated in FIG. 1.

Referring to FIG. 2, an AC power supply 10 comprises a commercial powersupply (not illustrated). An input terminal of a full-wave rectifyingcircuit 11 is connected to the AC power supply 10. The full-waverectifying circuit 11 generates output in which full-wave rectificationis performed to an AC power from the AC power supply 10. A ripplecurrent smoothing capacitor 12 is connected between positive andnegative output terminals of the full-wave rectifying circuit 11.

For example, a normally-on type field effect transistor 13 made of GaNis connected as a switching element constituting a step-down chopper tothe capacitor 12.

The field effect transistor 13 is formed by joining heterogeneoussemiconductor materials having different bandgaps. The field effecttransistor 13 comprises a two-dimensional electron gas layer at aninterface. The field effect transistor 13 can realize high-speedswitching and high sensitivity by an effect of the two-dimensionalelectron gas layer. The field effect transistor 13 is called an HEMT(High Electron Mobility Transistor).

In the field effect transistor 13, it is assumed that Vgs is agate-source voltage and Vth (negative voltage) is a threshold of a gatevoltage. The field effect transistor 13 is turned off for Vth>Vgs, andthe field effect transistor 13 is turned on for Vth<Vgs.

A drain of the field effect transistor 13 is connected to an outputterminal on a positive electrode side of the full-wave rectifyingcircuit 11. A source of the field effect transistor 13 is connected tothe output terminal on the positive electrode side of the full-waverectifying circuit 11 through an LED element group 14 and a seriescircuit of a resistive element 15 and an inductor 16. The LED elementgroup 14 comprises a plurality of series-connected LED elements as asemiconductor light emitting element. A gate of the field effecttransistor 13 is connected to a connection point of the resistiveelement 15 and the inductor 16 through a normally-off type field effecttransistor 18. The normally-off type field effect transistor 18 that isthe switching element constitutes a driving control unit.

A gate protecting diode 19 having a polarity illustrated in FIG. 2 isconnected between the source and the gate of the field effect transistor13.

The LED element group 14 corresponds to the LED illuminating lamps 2 and3 illustrated in FIG. 1. When a current is passed through the LEDelement group 14, a forward voltage having a polarity illustrated inFIG. 2 is generated at both ends of the LED element group 14. The fieldeffect transistor 13 is turned off by applying a negative potential ofthe forward voltage between the source and the gate of the field effecttransistor 13. A capacitor 20 is connected in parallel to the LEDelement group 14.

The inductor 16 comprises an auxiliary winding 161 that is coupledthereto. One end of the auxiliary winding 161 is connected to theconnection point of the resistive element 15 and the inductor 16. Theother end of the auxiliary winding 161 is connected to the gate of thefield effect transistor 18 through a diode 21 having a polarityillustrated in FIG. 2. Electromagnetic energy is accumulated and emittedat the inductor 16 in association with an on-off operation of the fieldeffect transistor 13, thereby generating the stepped-down DC output atboth ends of the capacitor 20 through a flywheel diode 22. Aself-excited circuit is configured to cause the field effect transistor18 to perform the on-off operation by the output of the auxiliarywinding 161 in synchronization with the accumulation and emission of theelectromagnetic energy at the inductor 16.

A comparator 23 constituting a constant current control unit isconnected to the resistive element 15. The comparator 23 is connected tothe gate of the field effect transistor 18 through a diode 24 having apolarity illustrated in FIG. 2. In the comparator 23, a power supply 17that generates a previously-set reference signal Vf is connected to oneof input terminals. A load current passed through the resistive element15 is input to the other terminal of the comparator 23. The comparator23 compares the input load current and the reference signal Vf. As aresult of the comparison, the comparator 23 forces the field effecttransistor 18 to perform the on operation when the load current reachesthe reference signal Vf.

Action of the first embodiment will be described below.

When the power supply is turned on with a power-supply switch (notillustrated), the forward voltage having the polarity illustrated inFIG. 2 is generated at both ends of the LED element group 14 through thefield effect transistor 13 in the on state. When the current passedthrough the LED element group 14 becomes the reference signal Vf of thecomparator 23 by turning on the field effect transistor 13, the fieldeffect transistor 18 is turned on, and the negative potential is appliedbetween the source and the gate of the field effect transistor 13 by theforward voltage of the LED element group 14. In such cases, Vth>Vgs isobtained to turn off the field effect transistor 13. At this point, theauxiliary winding 161 of the inductor 16 generates a signal tocontinuously turn on the field effect transistor 18. The field effecttransistor 18 is turned off when the discharge of the inductor 16 isended. In such cases, because of Vth<Vgs, the field effect transistor 13is turned on again.

The similar operation is repeated, and the field effect transistor 13 isturned on and off by a switching operation of the field effecttransistor 18. The stepped-down DC output is generated at both ends ofthe capacitor 20 through the flywheel diode 22 by the accumulation andemission of the electromagnetic energy at the inductor 16. The LEDelement group 14 is lit by the DC output.

When the load current passed through the resistive element 15 becomesthe previously-set reference signal Vf of the comparator 23, the fieldeffect transistor 18 is turned on while the field effect transistor 13is turned off. Therefore, the load current is restricted, the loadcurrent passed through the LED element group 14 is controlled so as tobe always matched with the reference signal Vf, and the constant currentcontrol is performed.

Accordingly, the normally-on type field effect transistor 13 is used asthe switching element constituting the step-down chopper, and the fieldeffect transistor 13 can be turned off by utilizing the forward voltagegenerated in the LED element group 14. Therefore, it is not necessarythat a special power-supply circuit be incorporated to obtain thenegative voltage used to turn off the normally-on type field effecttransistor 13, and the number of components can be decreased. Thecircuit configuration can be simplified, the device can be miniaturized,and cost can be reduced.

The proper negative potential of Vth>Vgs (gate-source voltage) isobtained with respect to the threshold Vth of the gate voltage of thefield effect transistor 13 by the forward voltage generated in the LEDelement group 14, so that the normally-on type field effect transistorcan securely be turned off.

The normally-on type field effect transistor 13 made of GaN is used asthe switching element. In the field effect transistor 13, high frequencycan be achieved without degrading the efficiency. Therefore, capacitiesof impedance elements such as the inductor and the capacitor whichconstitute the circuit can be decreased, and modularization can beachieved by the further compact apparatus.

The light control of the LED element group 14 can be performed bychanging the reference voltage Vf of the power supply 17 from anexternal manipulation. In such cases, for example, preferably areceiving circuit that receives a control signal is provided throughinsulating type input means such as a remote controller and aphotocoupler on a side of a substrate (not illustrated) on which the LEDelement group 14 is mounted.

The number of series-connected LED elements is restricted. Therefore,when at least the restricted number of LED elements is required as theLED illuminating lamp in order to optimally set the forward voltagegenerated at both ends of the LED element group 14, the LED elementsmore than the proper number of LED elements are series-connected to theinductor 16.

Second Embodiment

A second embodiment will be described below.

FIG. 3 illustrates a schematic configuration of the second embodiment.In FIG. 3, the same components as those of FIG. 2 are designated by thesame numerals.

In the second embodiment, a series circuit of normally-on type fieldeffect transistors 32 and 33 made of GaN is connected as the switchingelement to both ends of the capacitor 12 connected between the positiveand negative output terminals of the full-wave rectifying circuit 11.The series circuit of the field effect transistors 32 and 33 isseries-connected to an LED element group 31 comprising a plurality ofseries-connected LED elements as the semiconductor light emittingelement. While the threshold Vth of the gate voltage becomes negative,the field effect transistors 32 and 33 are turned off for Vth>Vgs(gate-source voltage) and turned on for Vth<Vgs. Diodes 32 a and 33 ahaving polarities illustrated in FIG. 3 are connected between thesources and the drains of the field effect transistors 32 and 33,respectively.

A capacitor 34 is parallel-connected to the series circuit of the fieldeffect transistors 32 and 33, and a series circuit of an inductor 35 anda capacitor 36 is parallel-connected to the field effect transistor 33.A diode 37 having a polarity illustrated in FIG. 3 is connected betweenthe gate and the source of the field effect transistor 32, and a firstdriving source 39 is connected to both ends of the diode 37 through acapacitor 38. A diode 40 having a polarity illustrated in FIG. 3 isconnected between the gate and the source of the field effect transistor33, and a second driving source 42 is connected to both ends of thediode 40 through a capacitor 41. The first and second driving sources 39and 42 output positive and negative pulse signals through the capacitors38 and 41, and first and second driving sources 39 and 42 alternatelyinput negative voltage signals, to which half-wave rectification isperformed by the diodes 37 and 40, between the gates and the sources ofthe field effect transistors 32 and 33.

A normally-on type field effect transistor 43 made of GaN is connectedas the switching element that is the driving control unit to theconnection point of the capacitor 12 and the LED element group 31. Inthe field effect transistor 43, the drain is connected to the connectionpoint of the capacitor 12 and the LED element group 31, and the sourceis connected to the gate of the field effect transistor 33 through thecapacitor 44. In the field effect transistor 43, the gate is connectedto the connection point of the capacitor 44 and the gate of the fieldeffect transistor 33. The field effect transistor 43 generates anegative potential at the capacitor 44 by the forward voltage of the LEDelement group 31 once the field effect transistor 43 is powered-on, andthe field effect transistor 43 inputs the negative potential to the gateof the field effect transistor 33. A diode 43 a having a polarityillustrated in FIG. 3 is connected between the source and the drain ofthe field effect transistor 43.

Action of the second embodiment will be described below.

When the power supply is turned on with a power-supply switch (notillustrated) to generate the forward voltage in the LED element group31, a charge current is passed through the capacitor 44 through thefield effect transistor 43 in the on state by the forward voltage,thereby charging the capacitor 44 in the polarity illustrated in FIG. 3.Therefore, the negative potential at the capacitor 44 is applied to thegate of the field effect transistor 33 to turn off the field effecttransistor 33. Accordingly, a short circuit caused by the LED elementgroup 31 during the power-on and the field effect transistors 32 and 33in the on state is blocked to prevent such a trouble that the LEDelement group 31 is broken due to the passage of overcurrent. Thecharges of the capacitor 44 are discharged through the diode 43 a of thefield effect transistor 43.

Then the negative voltage signals are alternately input between thegates and the sources of the field effect transistors 32 and 33 throughthe diodes 37 and 40 by the outputs from the first and second drivingsources 39 and 42. The field effect transistor 32 is turned on, and thenegative voltage signal is input to the gate of the field effecttransistor 33 by the second driving source 42 to turn off the fieldeffect transistor 33. Therefore, the current is passed from the positiveelectrode side of the full-wave rectifying circuit 11 to the LED elementgroup 31, the field effect transistor 32, the inductor 35, the capacitor36, and the negative electrode side of the full-wave rectifying circuit11, and the electromagnetic energy is accumulated in the inductor 35. Atthis point, when the negative voltage signal is input to the gate of thefield effect transistor 32 by the first driving source 39 to turn offthe field effect transistor 32, the electromagnetic energy of theinductor 35 continuously passes the charge current to the capacitor 36through the diode 33 a of the field effect transistor 33. Theabove-described operation becomes the operation of the step-down chopperin which the capacitor 36 is used as the output capacitor.

The field effect transistor 33 is turned on, and the negative voltagesignal is input to the gate of the field effect transistor 32 by thefirst driving source 39 to turn off the field effect transistor 32.Therefore, the charge current is eliminated, and the discharge currentis passed from the capacitor 36 through the inductor 35 and the fieldeffect transistor 33 to accumulate the electromagnetic energy in theinductor 35. At this point, when the negative voltage signal is input tothe gate of the field effect transistor 33 by the second driving source42 to turn off the field effect transistor 33, the electromagneticenergy of the inductor 35 is passed through the diode 32 a of the fieldeffect transistor 32 and the capacitor 34. When the similar operation isrepeated, the load current is continuously passed through the LEDelement group 31, and the LED element group 31 is lit by the loadcurrent.

Accordingly, once the power supply is powered-on, the charge current ispassed to the capacitor 44 through the normally-on type field effecttransistor 43 to charge the capacitor 44 by utilizing the forwardvoltage of the LED element group 31, and the normally-on type fieldeffect transistor 33 constituting the switching circuit can be turnedoff by the negative potential at the capacitor 44. The effect similar tothat of the first embodiment is obtained in the second embodiment.Because the short circuit caused by the turn-ons of the field effecttransistors 32 and 33 can be blocked during the power-on, the passage ofthe overcurrent through the LED element group 31 can securely beeliminated to prevent the trouble such as the breakage of the LEDelement group 31 before happens.

(Modification)

FIG. 4 illustrates a schematic configuration of a constant-voltagesource applied to the second embodiment. The constant-voltage sourceillustrated in FIG. 4 can be applied as the power supply to the secondembodiment. At this point, a drain of a normally-on type field effecttransistor 47 is connected to an end on a positive electrode side of aDC power supply 46, and a source of the field effect transistor 47 isconnected to an end on a negative electrode side of the DC power supply46 through a capacitor 48. A zener diode 49 having a polarityillustrated in FIG. 4 is connected between a gate of the field effecttransistor 47 and an end on the negative electrode side of the DC powersupply 46. The zener diode 49 generates a constant voltage by a zenereffect.

When the field effect transistor 47 is turned on, a constant voltage Vcis generated between both ends of the capacitor 48 by the Zener diode49, so that the constant voltage can be used as the power supply.

Third Embodiment

A third embodiment will be described below.

FIG. 5 illustrates a schematic configuration of the third embodiment. InFIG. 5, the same components as those of FIG. 2 are designated by thesame numerals.

In the third embodiment, a series circuit of normally-on type fieldeffect transistors 51 and 52 made of GaN, a full-bridge circuit, and aseries circuit of an LED element group 55 as the semiconductor lightemitting element are connected as the switching element to both ends ofthe capacitor 12 connected to the positive and negative output terminalsof the full-wave rectifying circuit 11. The series circuit ofnormally-on type field effect transistors 53 and 54 made of GaN isparallel-connected to the full-bridge circuit. The LED element group 55comprises a plurality of series-connected LED elements as thesemiconductor light emitting element. An inductor 65 is connectedbetween the connection point of the field effect transistors 51 and 52and the connection point of the field effect transistors 53 and 54.

While the threshold Vth of the gate voltage becomes negative, thenormally-on type field effect transistors 51 to 54 are turned off forVth>Vgs (gate-source voltage) and turned on for Vth<Vgs. Diodes 51 a to54 a having polarities illustrated in FIG. 5 are connected between thesources and the drains of the field effect transistors 51 to 54,respectively. Gate protecting diodes 56 to 59 are connected between thegates and the sources of the field effect transistors 51 to 54,respectively. A capacitor 60 is parallel-connected to a bridge circuitof the field effect transistors 51 to 54.

When the current is passed through the LED element group 55, the LEDelement group 55 generates the forward voltage having polarityillustrated in FIG. 5 at both ends thereof, and a side of a ground G isput into the negative potential by the forward voltage. At this point,the negative potential on the side of the ground G is set so as tobecome the thresholds Vth of the gate voltages at the field effecttransistors 51 to 54 or less.

The gates of the field effect transistors 51 and 54 are commonlyconnected and connected to the ground G through a normally-on type fieldeffect transistor 61 made of GaN as the driving control unit. Similarlythe gates of the field effect transistors 52 and 53 are commonlyconnected and connected to the ground G through a normally-on type fieldeffect transistor 62 made of GaN as the driving control unit.

Diodes 61 a and 62 a having polarities illustrated in FIG. 5 areconnected between the sources and the drains of the field effecttransistors 61 and 62, respectively. The field effect transistors 61 and62 and a driving source 63 constitute a switch driving unit 64. Thedriving source 63 is connected to the gates of the field effecttransistors 61 and 62, and the driving source 63 alternately inputs thenegative voltage signal to the gates of the field effect transistors 61and 62.

Resistive elements 65 and 66 put forward returns of the field effecttransistors 52 to 54 from the off state to the on state.

Action of the third embodiment will be described below.

When the power supply is turned on with a power-supply switch (notillustrated), the field effect transistors 51 to 54 are turned on togenerate the forward voltage having polarity illustrated in FIG. 5 inthe LED element group 55, and the side of the ground G is put into thenegative potential. At this point, the negative potential on the side ofthe ground G is applied to the gates of the field effect transistors 51to 54 through the field effect transistors 61 and 62 in the on state,and the field effect transistors 51 to 54 are turned off. Therefore, theshort circuit caused by the field effect transistors 51 to 54 and theLED element group 55 is blocked during the power-on.

Then the negative voltage signals are alternately input to the gates ofthe field effect transistors 61 and 62 by the output from the drivingsource 63 of the switch driving unit 64. The field effect transistors 51and 54 are turned on, the field effect transistor 62 is turned on, andthe negative potential on the side of the ground G is applied to thegates of the field effect transistors 52 and 53, thereby turning off thefield effect transistors 52 and 53. Therefore, the current is passedfrom the positive electrode side of the full-wave rectifying circuit 11through the field effect transistor 51, the inductor 65, the fieldeffect transistor 54, and the LED element group 55, and theelectromagnetic energy is accumulated in the inductor 65. At this point,the field effect transistor 61 is turned on, the negative potential onthe side of the ground G is applied to the gates of the field effecttransistors 51 and 54, and the field effect transistors 51 and 54 areturned off. Therefore, the electromagnetic energy of the inductor 65passes the charge current through the diode 53 a of the field effecttransistor 53, the capacitor 60 and the diode 52 a of the field effecttransistor 52.

The field effect transistors 52 and 53 are turned on, the field effecttransistor 61 is turned on, and the negative potential on the side ofthe ground G is applied to the gates of the field effect transistors 51and 54, thereby turning off the field effect transistors 51 and 54.Therefore, the discharge current is passed from the capacitor 60 throughthe field effect transistor 53, the inductor 65, and the field effecttransistor 52, and the electromagnetic energy is accumulated in theinductor 65. At this point, the field effect transistor 62 is turned on,the negative potential on the side of the ground G is applied to thegates of the field effect transistors 52 and 53, and the field effecttransistors 52 and 53 are turned off. Therefore, the electromagneticenergy of the inductor 65 is passed as the charge current through thediode 51 a of the field effect transistor 51, the capacitor 60 and thediode 54 a of the field effect transistor 54. When the similar operationis repeated, the load current is continuously passed through the LEDelement group 55, and the LED element group 55 is lit by the loadcurrent.

Accordingly, once the power supply is powered-on, the side of the groundG is set to the negative potential by the forward voltage of the LEDelement group 55, and the normally-on type field effect transistors 51to 54 constituting the switching circuit can be turned off by thenegative potential on the side of the ground G. The effect similar tothat of the first embodiment is obtained in the third embodiment.Because the short circuit caused by the turn-ons of the field effecttransistors 51 to 54 can be blocked during the power-on, the passage ofthe overcurrent through the LED element group 55 can securely beeliminated to prevent the trouble such as the breakage of the LEDelement group 55 before happens.

Fourth Embodiment

A fourth embodiment will be described below.

FIG. 6 illustrates a schematic configuration of the fourth embodiment.In FIG. 6, the same components as those of FIG. 2 are designated by thesame numerals.

In the fourth embodiment, similarly to the first embodiment, anormally-on type field effect transistor 71 made of GaN is connected asthe switching element constituting the step-down chopper to thecapacitor 12.

In the field effect transistor 71, the threshold Vth of the gate voltageis a negative voltage. The field effect transistor 71 is turned off forVth>Vgs (gate-source voltage), and the field effect transistor 71 isturned on for Vth<Vgs. The drain of the field effect transistor 71 isconnected to the output terminal on the positive electrode side of thefull-wave rectifying circuit 11. The source of the field effecttransistor 71 is connected to the output terminal on the positiveelectrode side of the full-wave rectifying circuit 11 through an LEDelement group 72 and a series circuit of a resistive element 73 and aninductor 74. The LED element group 72 comprises a plurality ofseries-connected LED elements as the semiconductor light emittingelement.

The LED element group 72 corresponds to the LED illuminating lamps 2 and3 illustrated in FIG. 1. When the load current is passed through the LEDelement group 72, the forward voltage having the polarity illustrated inFIG. 6 is generated at both ends of the LED element group 72. Acapacitor 75 is connected in parallel to the LED element group 72.

The inductor 74 comprises an auxiliary winding 741 that is coupledthereto. One end of the auxiliary winding 741 is connected to the gateof the field effect transistor 71 through the capacitor 76. The otherend of the auxiliary winding 741 is connected to the connection point ofthe field effect transistor 71 and the LED element group 72. Theelectromagnetic energy is accumulated and emitted at the inductor 74 inassociation with the on-off operation of the field effect transistor 71,thereby generating the stepped-down DC output at both ends of thecapacitor 75 through a flywheel diode 77.

A self-excited circuit is configured such that the field effecttransistor 71 is turned off by generating the negative potential ofVth>Vgs between the source and the gate of the field effect transistor71 from the output of the auxiliary winding 741 in synchronization withthe accumulation and emission of the electromagnetic energy at theinductor 74. For example, a normally-on type diode made of GaN is usedas the flywheel diode 77.

The gate of the field effect transistor 71 is connected to theconnection point of the resistive element 73 and the inductor 74 througha resistive element 78 that is a current-limiting resistance and anormally-off type field effect transistor 80 that is the switchingelement.

The field effect transistor 80, comparators 81 and 82, resistiveelements 83 and 84, and a power supply 85 constitute an oscillationstopping unit 79 that is the driving control unit. In the comparator 81,one of input terminals is connected to the connection point of the fieldeffect transistor 71 and the LED element group 72, and the other inputterminal is connected to the power supply 85, and the output terminal isconnected to the connection point of the resistive element 73 and theinductor 74 through the resistive elements 83 and 84.

The comparator 81 acts as an operational amplifier, and the comparator81 generates the reference signal Vf at the connection point of theresistive elements 83 and 84 in order to detect the state, in which theforward voltage (load voltage) at the LED element group 72 becomes lowerthan the threshold Vth by the setting of the power supply 85, as anabnormal state. In the comparator 82, one of input terminals isconnected to the connection point of the LED element group 72 and theresistive element 73, the other input terminal is connected to theconnection point of the resistive elements 83 and 84, and the outputterminal is connected to the gate of the field effect transistor 80. Thecomparator 82 turns on the field effect transistor 80 based on thecomparison result of the current passed through the resistive element 73and the reference signal Vf.

Diodes 86 and 87 constitute a gate voltage clamping circuit that clampsthe gate voltage at the field effect transistor 71. The gate voltage atthe field effect transistor 71 is clamped using the forward voltage atthe LED element group 72.

Action of the fourth embodiment will be described below.

When the power supply is turned on with a power-supply switch (notillustrated), the forward voltage having the polarity illustrated inFIG. 6 is generated at both ends of the LED element group 72 through thefield effect transistor 71 in the on state. When the field effecttransistor 71 is turned on, the current is passed to the inductor 74through the LED element group 72. Therefore, the electromagnetic energyis accumulated in the inductor 74 while the output is generated by theauxiliary winding 741, and the output is input to the gate of the fieldeffect transistor 71 through the capacitor 76. In such cases, thenegative potential of Vth>Vgs is generated between the source and thegate of the field effect transistor 71 by the output of the auxiliarywinding 741 to turn off the field effect transistor 71.

At this point, the electromagnetic energy accumulated in the inductor 74is emitted, the input from the auxiliary winding 741 is eliminated, andthe Vth<Vgs is obtained, thereby turning on the field effect transistor71.

The similar operation is repeated, and the field effect transistor 71 isturned on and off by the output of the auxiliary winding 741 insynchronization with the accumulation and emission of theelectromagnetic energy at the inductor 74. At the same time, thestepped-down DC output is generated at both ends of the capacitor 75through the flywheel diode 77 by the accumulation and emission of theelectromagnetic energy at the inductor 74. The LED element group 72 islit by the DC output.

On the other hand, the comparator 81 acts as the operational amplifierto output the reference signal Vf to the connection point of theresistive elements 83 and 84. At this point, the load current passedthrough the resistive element 73 according to the forward voltage (loadvoltage) of the LED element group 72 is input to the comparator 82. Thecomparator 82 compares the load current and the reference signal Vf. Thecomparator 82 generates the output to turn on the field effecttransistor 80, when a determination that the load current is smallerthan the reference signal Vf is made, that is, when a determination thatthe forward voltage (load voltage) at the LED element group 72corresponding to the load current is lower than the threshold Vth ismade from the comparison result. Therefore, the negative potential ofthe forward voltage at the LED element group 72 is applied between thesource and the gate of the field effect transistor 71, and the fieldeffect transistor 71 is turned off to stop the self-excited oscillation.

Accordingly, the effect similar to that of the first embodiment can alsobe obtained in the fourth embodiment. When the determination that theforward voltage (load voltage) at the LED element group 72 is lower thanthe threshold Vth is made, the field effect transistor 71 can forcedlybe turned off to stop the self-excited oscillation. Therefore, thecircuit protection can be realized such that the circuit can beprevented from going out of control due to the abnormal decrease of theforward voltage at the LED element group 72.

The self-excited oscillation can be stopped by changing the setting ofthe reference signal Vf, when the forward voltage (load voltage) at theLED element group 72 becomes higher than a predetermined forward voltage(load voltage).

The embodiment is not limited to the above embodiments, but variousmodifications can be made without departing from the scope at theimplementation phase. For example, in the embodiments, the normally-ontype field effect transistor made of GaN is applied. Alternatively,another wide-bandgap semiconductor made of SiC may be applied. In theembodiments, the LED element is used as the semiconductor light emittingelement. However, the embodiment can be applied to another semiconductorlight emitting element such as a laser diode.

In one embodiment, the power-supply device (LED lighting device) maycomprise a switching element that is formed by a normally-on type fieldeffect transistor, and a driving control unit that can turn off thefield effect transistor by applying the negative potential of Vth>Vgs(gate-source voltage) with respect to the threshold Vth of the gatevoltage at the field effect transistor using the forward voltagegenerated in the semiconductor light emitting element.

In one embodiment, the power-supply device may comprise a drivingcontrol unit that can turn off the field effect transistor when theforward voltage generated in the semiconductor light emitting element islower than the threshold Vth or higher than a predetermined voltage.

In one embodiment, the power-supply device may comprise a drivingcontrol unit that comprises a normally-on type field effect transistor.

According to the first to fourth embodiments, because the forwardvoltage generated in the semiconductor light emitting element is used toturn off the normally-on type switching element, it is not necessary toincorporate the particular circuit in the device, and the device can beminiaturized to reduce the cost.

According to the first to fourth embodiments, the proper negativepotential is obtained by the forward voltage generated in thesemiconductor light emitting element, so that the normally-on type fieldeffect transistor can securely be turned off.

According to the first to fourth embodiments, the self-excitedoscillation of the normally-on type field effect transistor can bestopped to realize the circuit protection.

Fifth Embodiment

An LED lighting device according to a fifth embodiment will be describedwith reference to FIG. 7.

The LED lighting device of the fifth embodiment comprises a DC powersupply DC, a chopper CH, a load circuit LC, and a control circuit CC.

The DC power supply DC may have any configuration. For example, the DCpower supply DC is mainly formed by a rectifying circuit DB, anddesirably the DC power supply DC may comprise a smoothing circuit thatcomprises a smoothing capacitor C1. In the fifth embodiment, preferablythe rectifying circuit DB is formed by a bridge-type rectifying circuit,and the rectifying circuit DB performs full-wave rectification of an ACvoltage of an AC power supply AC, for example, a commercial AC powersupply to obtain a DC voltage.

In the fifth embodiment, the chopper CH is formed by a non-isolated typestep-down chopper. A power unit of the chopper CH, that is, a circuitunit through which an electric power supplied to the load is passedcomprises a normally-on switch Q1, an inductor L1, a free-wheel diodeD1, and a current detecting impedance element Z1. The power unit can bedivided into a first circuit A and a second circuit B from the viewpointof circuit operation.

The first circuit A accumulates the electromagnetic energy in theinductor L1 from the DC power supply DC. The first circuit A has aconfiguration in which a series circuit including the normally-on switchQ1, the load circuit LC, and the inductor L1 is connected to the DCpower supply DC. When the normally-on switch Q1 is turned on, anincreased current is passed from the DC power supply DC to accumulatethe electromagnetic energy in the inductor L1.

The second circuit B emits the electromagnetic energy accumulated in theinductor L1. The second circuit B has a configuration in which a seriescircuit including the free-wheel diode D1 and the load circuit LC isconnected to the inductor L1. A decreased current is passed from theinductor L1 when the normally-on switch Q1 is turned off.

Various wide-gap semiconductors described in the background art can beused as the normally-on switch Q1. The HEMT in which a GaN substrate isutilized is used in the fifth embodiment. Accordingly, the normally-onswitch Q1 is a field effect wide-gap semiconductor that comprises adrain, a source, and a gate. The normally-on switch Q1 has an extremelyexcellent potential compared with a wide-spread Si semiconductor. Forexample, the chopper can be operated at an operating frequency as highas gigahertz. Therefore, because the extremely compact inductor L1 canbe implemented, the whole of the LED lighting device can extremely beminiaturized.

The inductor L1 accumulates the electromagnetic energy supplied from theDC power supply DC and emits the electromagnetic energy. Therefore,unlike the conventional technique, it is not necessary to provide asecondary winding. Accordingly, the structure of the inductor L1 can besimplified to contribute to the miniaturization.

The free-wheel diode D1 is a means for providing a current pathway, thatis, the second circuit B in order to emit and regenerate theelectromagnetic energy accumulated in the inductor L1. Switching diodessuch as a Schottky barrier diode and a PIN diode can be used as thefree-wheel diode D1 according to the operating frequency of the chopperCH.

The current detecting impedance element Z1 detects the increased currentand the decreased current while being inserted in a position on thecircuit through which both the increased current and the decreasedcurrent are passed, that is, a line portion that is shared by the firstcircuit A and the second circuit B. For example, the current detectingimpedance element Z1 is formed by a resistor having a small resistancevalue.

For a step-up chopper, the chopper CH can comprise the first circuit Aand the second circuit B. In the first circuit A, the series circuit ofthe inductor L1 and the normally-on switch Q1 is connected to the DCpower supply DC. In the second circuit B, the series circuit of theinductor L1, the free-wheel diode D1, and the load circuit LC isconnected to the DC power supply DC. For the step-up/step-down chopper,the chopper CH can be configured as described above.

The load circuit LC is formed by a parallel circuit of a light emittingdiode LED that is the load and an output capacitor C2. The load circuitLC is connected in a position on the circuit through which both theincreased current and the decreased current are passed. The single lightemitting diode LED is formed in the forward direction with respect tothe current, or the plurality of light emitting diodes LED are providedwhile series-connected.

The control circuit CC comprises a control switch CS and a matching unitMC. The control circuit CC is activated by the supply of a propercontrol power supply to perform on-off control of the normally-on switchQ1. In the fifth embodiment, the control power supply is supplied fromboth ends of the load circuit LC to the control circuit CC.

The control switch CS switches the turn-on and turn-off of thenormally-on switch Q1. That is, when the control switch CS is turned onto connect the gate of the normally-on switch Q1 to the connection pointof the impedance element Z1 and the inductor L1, the voltage that isnegative with respect to the source is applied to the gate of thenormally-on switch Q1, thereby turning off the normally-on switch Q1.The normally-on switch Q1 is turned on, when the control switch CS isturned off to open the connection of the gate of the normally-on switchQ1 to the connection point of the impedance element Z1 and the inductorL1, or when the potential at the normally-on switch Q1 becomes equal tothe potential at the source.

The matching unit MC is interposed between the impedance element Z1 andthe control switch CS, and the matching unit MC turns on the controlswitch CS when the increased current reaches a first predeterminedvalue. The matching unit MC turns off the control switch CS when thedecreased current reaches a second predetermined value.

Accordingly, when the terminal voltage at the impedance element Z1reaches the first predetermined value while the increased current ispassed, because the matching unit MC turns on the control switch CS, thenormally-on switch Q1 is turned off. When the terminal voltage at theimpedance element Z1 reaches the second predetermined value while thedecreased current is passed, because the matching unit MC turns off thecontrol switch CS, the normally-on switch Q1 is turned on.

A circuit operation will be described below.

When the DC power supply DC is powered on, the normally-on switch Q1 ofthe chopper CH is turned on to pass the current from the DC power supplyDC into the first circuit A, and the current is linearly increased. Thisis the increased current, and the electromagnetic energy is accumulatedin the inductor L1. When the increased current is passed into the firstcircuit A, the terminal voltage at the impedance element Z1 is increasedin proportion to the increased current. When the terminal voltagereaches the first predetermined value, the matching unit MC turns on thecontrol switch CS.

Because the gate of the normally-on switch Q1 becomes the negativevoltage when the control switch CS is turned on, the normally-on switchQ1 is turned off to cut off the increased current. Therefore, theelectromagnetic energy accumulated in the inductor L1 is emitted, thepassage of the current through the second circuit B is started tolinearly decrease the current. This is the decreased current. When thedecreased current reaches the second predetermined value, the matchingunit MC turns off the control switch CS.

Because the application of the negative voltage to the gate of thenormally-on switch Q1 is released when the control switch CS is turnedoff, the normally-on switch Q1 is turned on to start the passage of theincreased current again. The DC-DC conversion operation is continued byrepeating the above-described circuit operation.

Sixth Embodiment

An LED lighting device according to a sixth embodiment will be describedbelow with reference to FIG. 8.

The sixth embodiment differs from the fifth embodiment in the controlcircuit CC. In FIG. 8, the same components as those of FIG. 7 aredesignated by the same numerals, and the descriptions thereof areomitted.

In the control circuit CC of the sixth embodiment, the control switch CScomprises a P-type FET 1 and an N-type FET 2, which areparallel-connected. The connection point of the drain of the P-type FET1 and the source of the N-type FET 2 is connected to the gate of thenormally-on switch Q1.

The matching unit MC is formed by a hysteresis comparator CPh. In thehysteresis comparator CPh, an inverting input terminal is connected toone end on the side of the load circuit LC of the impedance unit Z1, anon-inverting input terminal is connected to a reference potential E,and an output terminal is connected to the gates of the P-type FET 1 andthe N-type FET 2. A feedback resistor R1 whose resistance value ispreviously adjusted is connected between the non-inverting inputterminal and the output terminal. The reference potential E is formed atthe connection point of the load circuit LC and a voltage divider VD.The voltage divider VD comprises resistors R2 and R3 that areparallel-connected to a series portion of the impedance unit Z1.

When the terminal voltage at the impedance unit Z1 reaches the firstpredetermined value while the normally-on switch Q1 is turned on to passan increased current IU through the impedance unit Z1, a positive firstpredetermined voltage is input to the inverting input terminal of thehysteresis comparator CPh, and a negative maximum output voltage isoutput to the output terminal. Because the negative maximum outputvoltage is applied to the gate of the P-type FET 1 of the control switchCS, the P-type FET 1 is turned on. At this point, the N-type FET 2remains in the off state.

Because the gate of the normally-on switch Q1 becomes the negativepotential when the P-type FET 1 is turned on, the normally-on switch Q1is turned off to cut off the increased current IU. Therefore, adecreased current ID is passed from the inductor L1. Because theterminal voltage at the impedance unit Z1 in passing the decreasedcurrent ID is input to the inverting input terminal of the hysteresiscomparator CPh after the terminal voltage of the increased current, whenthe terminal voltage at the impedance unit Z1 reaches the secondpredetermined value, a positive maximum voltage is output from theoutput terminal of the hysteresis comparator CPh. As a result, theP-type FET 1 is turned off while the N-type FET 2 is turned on.

When the P-type FET 1 is turned off while the N-type FET 2 is turned on,the normally-on switch Q1 is turned on, whereby the increased current ispassed through the load circuit LC again. The chopper operation isperformed by repeating the above-described operation.

A relationship between a current and a voltage waveform in each unit ofthe sixth embodiment will be described with reference to FIG. 9. A part(a) of FIG. 9 illustrates a waveform of the increased current IU, a part(b) illustrates a waveform of the decreased current ID, a part(c)illustrates a waveform of a terminal voltage VZ1 at the impedance unit,a part (d) illustrates a waveform of a voltage VL1 at the inductor, anda part (e) illustrates a waveform of a gate voltage VGS at thenormally-on switch. In the parts (a) to (e) of FIG. 9, time axes arematched with one another. In FIG. 9, a peak value of the increasedcurrent IU corresponds to the case where the increased current IUreaches the first predetermined value. The value of zero of thedecreased current ID corresponds to the case where the decreased currentID reaches the second predetermined value.

The current waveform chart of FIG. 9 is an ideal waveform when the delayis not generated in the control. However, when a considerable delay isgenerated in the control during the cut-off of the increased current,the first predetermined value is located at a position that is lowerthan the peak value by a value corresponding to the control delay. Inthe state in which the decreased current reaches the secondpredetermined value, when a considerable delay is generated in thecontrol, a current cut-off time corresponding to the control delay isgenerated between the decreased current and the next increased current.

Seventh Embodiment

An LED lighting device according to a seventh embodiment will bedescribed below with reference to FIG. 10.

The seventh embodiment differs from the fifth and sixth embodiments inthe control circuit CC. In FIG. 10, the same components as those of FIG.7 are designated by the same numerals, and the descriptions thereof areomitted.

The control switch CS is mainly formed by a bipolar transistor Q2. Inthe bipolar transistor Q2, a collector is connected to the gate of thenormally-on switch Q1 and connected to the source of the normally-onswitch Q1 through a control power supply Vdd formed by a dropper, and anemitter is connected to the connection point of the inductor L1 and theimpedance unit Z1.

The matching unit MC is mainly formed by a bipolar transistor Q3 andresistors R4 and R5. In the bipolar transistor Q3, the collector isconnected to the base of the bipolar transistor Q2 of the control switchCS through the resistor R4, the emitter is connected to the connectionpoint of the inductor L1 and the impedance unit Z1, and the base isconnected to the collector of the bipolar transistor Q2 through aresistor R6. The series circuit of the resistors R5 and R4 and thecollector and the emitter of the bipolar transistor Q3 isparallel-connected to the impedance unit Z1.

When the normally-on switch Q1 is turned on to pass the increasedcurrent, the bipolar transistor Q2 of the control switch CS is turnedoff, and the bipolar transistor Q3 of the matching unit MC is turned on.Therefore, the terminal voltage at the impedance unit Z1 is divided bythe series circuit of the resistor R4 and the resistor R5, and thevoltage at both ends of the resistor R4 is applied between the base andthe emitter of the bipolar transistor Q2.

Therefore, the values of the resistors R4 and R5 are previously adjustedto relatively set the resistor R4 to a smaller value, whereby thebipolar transistor Q2 can be configured to become the off state at alevel in which the increased current does not reach the firstpredetermined value. However, when the increased current reaches thefirst predetermined value, the bipolar transistor Q2 becomes the onstate, and the negative voltage is applied to the gate of thenormally-on switch Q1. Therefore, the normally-on switch Q1 is turnedoff to cut off the increased current.

Because the bipolar transistor Q3 is turned off when the bipolartransistor Q2 becomes the on state, when the normally-on switch Q1 isturned off to pass the decreased current, the terminal voltage at theimpedance unit Z1 is applied to the bipolar transistor Q2 withoutdividing the terminal voltage, and the bipolar transistor Q2 maintainsthe on state. However, when the terminal voltage at the impedance unitZ1 is decreased to reach the second predetermined value, the bipolartransistor Q2 is turned off because the bipolar transistor Q2 cannotmaintain the on state. As a result, the normally-on switch Q1 is turnedon again. The chopper operation is continued by repeating theabove-described circuit operation.

In the seventh embodiment, the chopper includes various choppers such asa step-down chopper, a step-up chopper, and a step-up/step-down chopper.The step-up/step-down chopper is formed by sequentially connecting thestep-up chopper and the step-down chopper. In each chopper, theincreased current is passed through the inductor from the DC powersupply by turning on the normally-on switch, and the electromagneticenergy accumulated in the inductor is emitted by turning off thenormally-on switch and the decreased current is passed to perform thechopper operation.

In the seventh embodiment, the control circuit comprises the controlswitch and the matching unit.

The control switch comprises at least a switch that switches thenormally-on switch from the on state to the off state. Desirably thecontrol switch may comprise a second switch that switches thenormally-on switch from the off state to the on state. In such cases,the switch that switches the normally-on switch from the on state to theoff state becomes a first switch.

The matching unit is interposed between the impedance unit and thecontrol switch. The matching unit operates the control switch to turnoff the normally-on switch, when the terminal voltage at the impedanceunit reaches the first predetermined value while the increased currentis passed through the impedance unit. The matching unit controls thecontrol switch to turn on the normally-on switch, when the terminalvoltage at the impedance unit reaches the second predetermined valuewhile the decreased current is passed. The second predetermined value islower than the first predetermined value.

There is no particular limitation to the matching unit as long as thematching unit has the above-described functions. Preferably the matchingunit can be formed by a hysteresis comparator. Alternatively, thematching unit comprises a first detection unit that directly detects theterminal voltage at the impedance unit and a second detection unit thatdetects the terminal voltage through a voltage divider, and the controlswitch may switch the second detection unit to the first detection unitin conjunction with the turn-off of the normally-on switch.

When the normally-on switch is turned on, the increased current ispassed from the DC power supply to the inductor. When the terminalvoltage at the impedance unit reaches the first predetermined value, thecontrol switch is turned on to apply the negative voltage to the gate ofthe normally-on switch through the matching unit. Therefore, thenormally-on switch is turned off to cut off the increased current. Theelectromagnetic energy accumulated in the inductor is emitted inassociation with the cut-off of the increased current, the decreasedcurrent is passed from the inductor, and the control switch is turnedoff to release the application of the negative voltage to the gate ofthe normally-on switch through the matching unit, thereby turning on thenormally-on switch. The chopper operation is performed by repeating theabove-described circuit operation.

Because the load circuit is connected to the position on the circuitthrough which both the increased current and the decreased current arepassed in association with the chopper operation, the DC-DC voltageconversion is performed, and the constant current control is performedunder the converted voltage to light the light emitting diode having theload connected to the output end. The output capacitor that isparallel-connected to the light emitting diode of the load circuit isoperated so as to bypass a high-frequency component included in theoutput of the chopper from the light emitting diode. As a result, thelight emitting diode is lit by the smoothed DC current.

In the seventh embodiment, there is no particular limitation to thesupply of the control power supply to the control circuit. Preferablythe control power supply is obtained from the load circuit or thehigh-voltage side of the normally-on switch. In the mode in which thecontrol power supply is obtained from the load circuit, because the DCvoltage smoothed by the output capacitor is generated in the loadcircuit, a voltage that is higher than the gate threshold voltage of thenormally-on switch is taken out from the load circuit to obtain thecontrol power supply, which allows the simplification of the circuitconfiguration of the control power supply. In the mode in which thecontrol power supply is obtained from the high-voltage side of thenormally-on switch, for example, a voltage that is higher than the gatethreshold voltage of the normally-on switch can be obtained from thedrain side of the normally-on switch through the dropper.

In the seventh embodiment, the illuminating device means all the devicesin which the light emitting diode is used as the light source.Accordingly, the illuminating device may be an illuminating apparatus, adisplay device, and a sign device. The illuminating device main bodymeans a residual portion in which the LED lighting device is removedfrom the illuminating device.

According to the fifth to seventh embodiments, the normally-on switch isused as the main switching element of the chopper, and the LED lightingdevice comprises the switch and the control circuit. The switch controlsthe normally-on switch to become the off state by applying the negativevoltage to the gate of the normally-on switch at least when thenormally-on switch is turned on, and the switch controls the normally-onswitch to become the on state by releasing the application of thenegative voltage to the gate of the normally-on switch when thenormally-on switch is turned off. The control circuit is interposedbetween the impedance element and the control switch. The controlcircuit turns on the control switch when the terminal voltage at theimpedance element reaches the first predetermined value while theincreased current is passed. The control circuit turns off the controlswitch when the terminal voltage at the impedance element reaches thesecond predetermined value that is lower than the first predeterminedvalue while decreased current is passed. Therefore, the simple circuitconfiguration is obtained without providing the secondary winding in theinductor, and the easy-to-integrate chopper having the goodcharacteristic and the illuminating device provided with the chopper canbe provided.

Eighth Embodiment

FIG. 11 illustrates an eighth embodiment. An LED lighting device of theeighth embodiment comprises the DC power supply DC, the chopper CH, andthe load circuit LC.

The DC power supply DC is a means for inputting the DC voltage ofpre-conversion to the chopper CH. Any configuration may be adopted inthe DC power supply DC as long as the DC voltage is outputted. Forexample, the DC power supply DC is mainly formed by a rectifying circuitDB, and desirably the DC power supply DC may comprise a smoothingcircuit that is formed by a smoothing capacitor and the like. In theeighth embodiment, preferably the rectifying circuit DB is formed by abridge type rectifying circuit, and the rectifying circuit DB performsthe full-wave rectification to the AC voltage of the AC power supply AC,for example, the commercial AC power supply to obtain the DC voltage.

In the eighth embodiment, the chopper CH comprises DC input ends t1 andt2 and DC output ends t3 and t4. The chopper CH comprises one of variouschoppers such as the step-down chopper, the step-up chopper, and thestep-up/step-down chopper. In each of configurations of variouschoppers, the chopper CH commonly comprises a switching element Q11, aconstant-current unit CCM, an inductor L11, a diode D11, and a drivingwinding DW.

The switching element Q11 is formed by either a normally-off switch or anormally-on switch. The constant-current unit CCM is formed by either aconstant-current unit in which the constant current value is previouslyfixed or a constant-current unit in which the constant current value isvariable. One end of the inductor L11 is connected to the drivingwinding DW. The driving winding DW is magnetically coupled to theinductor L11. The driving winding DW induces a voltage proportional tothe terminal voltage at the inductor L11 and applies the voltage to thecontrol terminal of the switching element Q11 to drive the switchingelement Q11.

The chopper CH comprises a pair of the input ends t1 and t2 and a pairof the output ends t3 and t4, and an internal circuit of the chopper CHcan be divided into a third circuit and a fourth circuit from theviewpoint of circuit operation. The third circuit passes the increasedcurrent from the DC power supply DC to accumulate the electromagneticenergy in the inductor L11. For the step-down chopper, the third circuithas a configuration in which the series circuit including the switchingelement Q11, the constant-current unit, the inductor L11, and the loadcircuit LC is connected to the DC power supply DC. In the third circuit,when the switching element Q11 is turned on, the increased current ispassed from the DC power supply DC to accumulate the electromagneticenergy in the inductor L11.

The fourth circuit emits the electromagnetic energy, accumulated in theinductor L11, to pass the decreased current. For the step-down chopper,the fourth circuit has a configuration in which the series circuitincluding the diode D11 and the load circuit LC is connected to theinductor L11, and the decreased current is passed from the inductor L11when the switching element Q11 is turned off.

For the step-up chopper, the chopper CH comprises the third circuit inwhich the series circuit of the inductor L11, the switching element Q11,and the constant-current unit CCM is connected to the DC power supply DCand the fourth circuit in which the series circuit of the inductor L11,the diode D11, and the load circuit LC is connected to the DC powersupply DC. For the step-up/step-down chopper, the chopper CH isconfigured as described above.

The load circuit LC comprises the light emitting diode that becomes theload and the parallel-connected output capacitor that bypasses thehigh-frequency component. For the step-down chopper, the load circuit LCis connected in the position on the circuit through which both theincreased current and the decreased current are passed. For the step-upchopper, the load circuit LC is connected in the position on the circuitthrough which the decreased current is passed. The single light emittingdiode LED is formed in the forward direction with respect to the currentpassed through the output end of the chopper, or the plurality of lightemitting diodes LED are provided while series-connected.

Ninth to twelfth embodiments will be described with reference to FIGS.12 to 17. In FIGS. 12 to 17, the same components as those of FIG. 11 aredesignated by the same numerals, and the descriptions thereof areomitted.

Ninth Embodiment

The ninth embodiment will be described below.

FIG. 12 illustrates the ninth embodiment. In the ninth embodiment, aGaN-HEMT is used as the switching element Q11, a constant-current diodeis used as the constant-current unit CCM, and the inductor L11 isconnected between the constant-current unit CCM and the load circuit LC.In FIG. 12, the same components as those of FIG. 11 are designated bythe same numerals, and the descriptions thereof are omitted. Ahigh-frequency bypass capacitor C11 is connected between the input endst1 and t2 of the chopper CH. A coupling capacitor C12 is insertedbetween the driving winding DW and the control terminal of the switchingelement Q11. The letter C designates the third circuit, and the letter Ddesignates the fourth circuit. The letter LED of the load circuit LCdesignates the light emitting diode, and the numeral C13 designates theoutput capacitor.

A circuit operation of the ninth embodiment will be described withreference to FIGS. 12 and 13.

Because the switching element Q11 of the chopper CH is turned on whenthe DC power supply DC is powered on, the current is passed from the DCpower supply DC to the third circuit C through the switching element Q11and the constant-current unit CCM, and the current is linearlyincreased. Therefore, the electromagnetic energy is accumulated in theinductor L11. The gate-source voltage VGS at the switching element Q11becomes zero while the switching element Q11 is turned on. When theincreased current reaches the constant current value of theconstant-current unit CCM, the increasing tendency of the current isstopped, and the current is kept constant. While the increased currentis passed through the inductor L11, the terminal voltage at the inductorL11 has the positive polarity as illustrated in a part (e) of FIG. 13.

When the increased current reaches the constant current value of theconstant-current unit CCM, because the current passed through theinductor L11 is further increased, the voltage VCCM at theconstant-current unit CCM is increased in the pulse shape as illustratedin a part (a) of FIG. 13. Therefore, the source potential at theswitching element Q11 becomes higher than the potential at the controlterminal (gate). As a result, because the control terminal relativelyand clearly becomes the negative potential, the switching element Q11 isturned off. Accordingly, the increased current IU passed through theinductor L11 is cut off by the turn-off of the switching element Q11 asillustrated in a part (b) of FIG. 13.

At the same time as the switching element Q11 is turned off, theemission of the electromagnetic energy accumulated in the inductor L11is started to pass the decreased current to the fourth circuit D asillustrated in a part (c) of FIG. 13. While the decreased current ispassed, the voltage polarity of the inductor L11 is inverted asillustrated in a part (e) of FIG. 13 to become the negative polarity,and the voltage is induced in the driving winding DW such that thecontrol terminal of the switching element Q11 becomes the negativepotential. At this point, as illustrated in a part (f) of FIG. 13,because the negative voltage is applied between the gate and the sourceof the switching element Q11 through the constant-current unit CCM, theswitching element Q11 is maintained in the off state.

When the decreased current passed through the third circuit C becomeszero, the negative voltage applied to the control terminal of theswitching element Q11 is not induced while the voltage in which thecontrol terminal becomes positive as illustrated in the part (e) of FIG.13 is induced in the driving winding DW by a counter-electromotiveforce. Therefore, the switching element Q11 is turned on again. Then thesimilar circuit operation is repeated.

As is clear from the circuit operation, the chopper CH performs thestep-down chopper operation, the output current Io in which theincreased current and the decreased current are alternately passedthrough the load circuit LC connected between the output ends t3 and t4is formed as illustrated in a part (d) of FIG. 13, the light emittingdiode LED is lit by the DC component, and the output capacitor C4bypasses the high-frequency component.

Tenth Embodiment

A tenth embodiment will be described below.

FIG. 14 illustrates the tenth embodiment. In the tenth embodiment, aGaN-HEMT is used as the constant-current unit CCM, and the inductor L11is connected to a position at which the load circuit LC is interposedbetween the constant-current unit CCM and the inductor L11.

In the constant-current unit CCM, the gate potential can be changed withan adjustable potential source E1, which allows the constant currentvalue to be changed. In FIG. 14, a diode ZD1 clamps the gate-sourcevoltage VGS at the switching element Q11 such that the gate-sourcevoltage VGS does not become 0.6 V or more.

In the tenth embodiment, the switching element Q11, the constant-currentunit CCM, and the diode D11, which constitute a series connection body,are formed as an integrated circuit IC. The integrated circuit ICcomprises first to fifth external terminals P1 to P5. The first externalterminal P1 is led out from the drain of the switching element Q11. Thesecond external terminal P2 is led out from a cathode of the diode D11.The third external terminal P3 is led out from the connection point ofthe source of the constant-current unit CCM and an anode of the diodeD11. The fourth external terminal P4 is led out from the gate of theswitching element Q11. The fifth external terminal P5 is led out fromthe gate of the constant-current unit CCM.

In the integrated circuit IC, the first and second main terminals areled out from the main terminals of the semiconductor element located atboth ends of a series connection body comprising three power-systemsemiconductor elements of the chopper, the third external terminal isled out from the main terminal of the intermediate connection portion ofthe series connection body, and the fourth and fifth external terminalsare led out from the switching element Q11 and the control terminal ofthe constant-current unit CCM. Accordingly, the first to third externalterminals are used for the power system, and the fourth and fifthexternal terminals are used for the control system.

In the tenth embodiment, because the constant-current unit CCM is formedby the GaN-HEMT similarly to the switching element Q11, the high-speedswitching characteristic is further improved at a high frequency of 10MHz or more. Desirably the diode D11 is made of a GaN material.Therefore, an integrated circuit can integrally be formed using the GaNsubstrate, extremely-high-speed switching is performed and the extremelycompact chopper is easily formed.

Because the constant current value can be changed using the adjustablepotential source E1, the desired load current is easily set.Additionally, when feedback control of the adjustable potential sourceE1 is performed with respect to a variation in power supply voltage, avariation in optical output of the light emitting diode can besuppressed with respect to the variation in power supply voltage.Further, the voltage drops of the constant-current unit CCM and the loadcircuit LC are added to the negative voltage of the driving winding DW,which applies to the control terminal of the switching element Q11.

Eleventh Embodiment

An eleventh embodiment will be described below.

FIG. 15 illustrates a schematic configuration of the eleventhembodiment. In FIG. 15, the same components as those of FIG. 12 aredesignated by the same numerals. In the eleventh embodiment, theconstant-current unit CCM is formed by a current mirror constant-currentcircuit in which transistors Q12 and Q13 are used. In the current mirrorconstant-current circuit, the series circuit of the transistor Q12 andthe resistor R11 is inserted in series with the switching element Q11,the base of the transistor Q12 is connected to the base of thetransistor Q13, and emitter is connected to a bias power supply E2 in areversed polarity manner, and a DC power supply E3 is connected to theseries circuit of the collector and the bias power supply E2. Thecollector and the base of the transistor Q13 are directly connected by aconductor.

A pair of zener diodes ZD1 and ZD2 is parallel-connected in the reversedpolarity manner between the control terminal of the switching elementQ11 and the position that steps over the constant-current unit CCM,thereby forming a clamp circuit. The zener diode ZD1 has a zener voltageof −12 V, and the zener diode ZD2 has a zener voltage of +0.7 V. Thezener diodes ZD1 and ZD2 protect the switching element Q11 such that theexcess voltage VGS is not applied to the switching element Q11.

According to the eleventh embodiment, the constant current value passedthrough the transistor Q12 can desirably be controlled by the DC voltageconnected to the transistor Q13, and the voltage generated in reachingthe constant current value is increased. Therefore, it is not necessaryto utilize the voltage at the light emitting diode LED that is the load.

The DC power supply E2 is used to control the constant current value ofthe constant-current unit CCM. Therefore, the transistor in whichhigh-speed control can be performed is not required. When theconstant-current unit CCM is turned off in synchronization with theturn-off of the switching element Q11, the switching element Q11 cansubstantially be used as the normally-off switching element. Desirablythe semiconductor component portions of the switching element Q11, theconstant-current unit CCM, and the diode D11 can be integrated into aGaN chip.

Twelfth Embodiment

A twelfth embodiment will be described below.

FIGS. 16 and 17 illustrate the twelfth embodiment. FIG. 16 is aschematic diagram of the integrated circuit module of the twelfthembodiment in which the LED lighting device is implemented. FIG. 17 is apartially enlarged and sectional perspective view schematicallyillustrating a planar coil structure.

In the twelfth embodiment, a semiconductor component, a coil component,a capacitor component, and an external terminal of the LED lightingdevice are mainly integrated in a part of or the plurality of eighth toeleventh embodiments. That is, the residual circuit components exceptthe light emitting diode LED of the LED lighting device are formed whiledivided into planar structures. The planar structures comprise a planarcoil structure L, a planar capacitor structure C, a GaN chip G, a wiringformation body W, a terminal formation body T, and a substrateconstruction body B. The planar structures are integrally stacked andconnected to each other using a means such as a through-hole, therebyforming an integrated circuit module IC. The integrated circuit moduleIC of FIG. 16 is roughly formed by the following planar structures.

As illustrated in FIG. 17, in the planar coil structure L, each of theinductor L11 and the driving winding DW is formed by winding a flat coilwire into a spiral shape in a plane. The flat coil wire formed into thespiral shape is retained such that the wires are properly separated fromone another, and the inside and the surround are coated with a magneticlayer M. Therefore, the planar coil structure L is formed into a planarshape as a whole.

One end of each of the inductor L11 and the driving winding DW islocated in a central portion of the coil to constitute a terminalportion t. A through-hole h is made in the center of the terminalportion t, one of terminal conductors of a constant-current unit portionof the GaN chip G is inserted in the through-hole h, and a conductivematerial is injected in the through-hole h to collectively connectconnection conductors of the inductor L11, the driving winding DW, andthe GaN chip G. As illustrated in a partially enlarged section on theright of FIG. 17, for example, the magnetic layer M is made of ceramicsor plastic in which ferrite fine particles are dispersed.

The planar capacitor structure C comprises a pair of electrodes thatsandwich a thin dielectric film therebetween and a plurality ofcapacitors are collected in the planar capacitor structure C.

The GaN chip G is a planar structure in which the switching element Q11,the constant-current unit CCM, and the diode D11 are formed in the GaNsemiconductor substrate.

The wiring formation body W is a planar structure that connects theterminal formation body T and the planar coil structure L, the planarcapacitor structure C, the GaN chip G.

The terminal formation body T is interposed between the wiring formationbody W and the substrate construction body B to connect the wiringformation body W and the substrate construction body B.

The substrate construction body B comprises an external terminal TE andan external attaching unit (not illustrated), and the substrateconstruction body B integrally supports the planar structures to achievethe modularization. The external terminal TE comprises an input terminalof the LED lighting device and an output terminal to which the lightemitting diode LED is connected.

The twelfth embodiment is suitable to the LED lighting device that isoperated at a high frequency of 10 MHz or more, and the externalterminal TE provided in the substrate construction body B is used onlyfor the DC. Therefore, the operation is stable and the miniaturizationcan significantly be realized due to only input and output of the DC.Accordingly, the LED lighting device can be provided between the lightemitting diodes of the illuminating device, which contributes to thesignificant miniaturization of the illuminating device.

In one embodiment, the LED lighting device comprises a series connectionbody of the switching element, the constant-current unit, and the diode.The series connection body comprises an integrated circuit, theintegrated circuit comprises first and second external terminals, athird external terminal, and fourth and fifth external terminals. Thefirst and second external terminals are led from a pair of mainterminals located on both end sides of the series connection body. Thethird external terminal is led from a main terminal located in theintermediate connection portion of the series connection body. Thefourth and fifth external terminals are led from the switching elementand the control terminal of the constant-current unit.

In the embodiments, the “chopper” is a concept including variouschoppers such as the step-down chopper, the step-up chopper, and thestep-up/step-down chopper. The step-up/step-down chopper is formed bysequentially connecting the step-up chopper and the step-down chopper.In each chopper, the increased current is passed through the inductorfrom the DC power supply by turning on the switching element, and theelectromagnetic energy accumulated in the inductor is emitted to passthe decreased current through the diode by turning off the switchingelement. The chopper operation is repeatedly performed to perform theDC-DC conversion of the DC power supply voltage, and the convertedvoltage is output to the output end.

The switching element may be either the normally-on switch or thenormally-off switch. When the wide-bandgap semiconductor, for example,the GaN-HEMT is used as the switching element, the switchingcharacteristic is extremely improved to lower a switching loss at a highfrequency of 10 MHz or more, and the inductor is also miniaturized.Therefore, the LED lighting device can significantly be miniaturized.

For the switching element in which the wide-bandgap semiconductor isused, the switching element having the normally-on characteristic ismore easily obtained, and the switching element is less inexpensive.However, the switching element having normally-off characteristic may beused because the switching element having normally-off characteristiccan also be obtained. The normally-on switch having a negative switchingthreshold is suitably used because the off control is easily performedusing the driving winding that is magnetically coupled to the inductor.

The constant-current unit has the constant current characteristic. Forexample, various constant-current circuits in which a constant-currentdiode, a junction FET, a three-terminal regulator, and a transistor areused can be used as the constant-current unit. A well-knownconstant-current circuit in which one or two transistors are used may beused as the constant-current circuit in which the transistor is used.The GaN-HEMT that is a kind of the junction FET can be used as theconstant-current circuit. Because the switching element has an excellentswitching characteristic at a high frequency of 10 MHz or more, theswitching element is suitably used to perform the high-speed switching.

The constant-current unit is disposed in the first circuit whileseries-connected to the switching element. In the first circuit, thecurrent is passed through the inductor when the switching element isturned on. The constant-current unit is also disposed in the drivingcircuit of the switch element comprising the driving winding that drivesthe switching element. Therefore, when the increased current passedthrough the constant-current unit is further increased after reachingthe constant current value, because the voltage at the constant-currentunit is rapidly increased, the potential at the main terminal (forexample, source) incorporated in the driving circuit of the switchingelement can be set relatively higher than the potential at the controlterminal (for example, gate) by the voltage increase generated in theconstant-current unit. As a result, the potential at the controlterminal becomes lower than the threshold of the switching element, sothat the switching element can be turned off. The circuit operation ismore easily and securely performed because the switching element is thenormally-on switch having the negative threshold. However, the circuitoperation is also effectively performed in the normally-off switch.

The switching element and the constant-current unit are permitted to bedirectly series-connected. In such cases, it is easy to integrate theswitching element and the constant-current unit in the commonsemiconductor chip, for example, the GaN chip. At this point, theswitching element and the constant-current unit can be formed by an ICmodule having a four-terminal structure. The IC module comprises: one ofmain terminals of the switching element, for example, the drain; twopower-system terminals formed by the main terminals on the other endside with respect to the switching element of the constant-current unit;and two control-system terminals formed by the control terminals of theswitching element and the constant-current unit, for example, the gates.Therefore, the single component can further be miniaturized.

The inductor accumulates the electromagnetic energy therein when theincreased current is passed from the DC power supply to the firstcircuit through the switching element and the constant-current unit.When the switching element is turned off, because the inductor emits theaccumulated electromagnetic energy, the decreased current is passedthrough the second circuit.

When the chopper is operated at a high frequency of 10 MHz or more, theinductor and the driving winding magnetically coupled to the inductorare formed into the planar coil structure, and the capacitor is formedinto the planar structure. Therefore, the integrated circuit of thechopper is advantageously achieved, and the high-reliability operationis obtained. Namely, the integrated circuit module can be formed bystacking and integrating the inductor and driving winding having theplanar coil structure, the capacitor having the planar structure, andthe semiconductor chip in which the semiconductor components such as theswitching element, the constant-current unit, and the diode areintegrated. As a result, the significantly compact LED lighting devicecan be achieved. Therefore, because a distance between the driving coiland the switch becomes the shortest, generation of unnecessary andharmful parasitic inductance or parasitic capacitance, which causesnoise generation, can be suppressed to the minimum level to improve thestability and reliability of the chopper operation.

The diode provides the second circuit that is the pathway when thedecreased current is passed from the inductor. When the wide-bandgapsemiconductor, for example, the GaN diode is used as the diode, thehigher-speed switching can be realized. In such cases, the diode iseasily formed as the integrated circuit of the semiconductor elementalong with the switching element and the constant-current unit. Theintegrated circuit has the structure having the five external terminalsin the series connection body of the switching element, theconstant-current unit, and the diode. The five external terminalscomprise the three power-system main terminals and the two controlterminals. The three power-system main terminals comprise the mainterminal on one end side of the series connection body, the mainterminal on the other end side, and the main terminal of theintermediate connection point. The two control terminals are used tocontrol the switching element and the constant-current unit,respectively.

When the chopper is formed by the integrated circuit, the whole isfurther miniaturized, and the high-speed switching is easily performed.

The driving winding is magnetically coupled to the inductor, and thedriving winding controls the switching element. When the increasedcurrent passed through the inductor in turning on the switching elementreaches the constant current value of the constant-current unit to turnoff the switching element, because the large voltage is generated, thepotential at the main terminal (source) of the switching element becomeshigher than the potential at the control terminal, and the controlterminal relatively becomes the negative potential to fall below thethreshold. Therefore, the switching element is maintained in the offstate.

According to the eighth to twelfth embodiments, the switching element isturned off by the voltage generated in the constant-current unit whenthe increased current passed from the DC power supply to the inductorthrough the constant-current unit in turning on the switching elementreaches the constant current value of the constant-current unit.Therefore, when the increased current reaches the predetermined value,the switching element can be turned off to perform the chopper operationby the simple configuration without providing a current feedback typefeedback circuit. The current feedback type feedback circuit comprisesthe impedance unit, such as the resistive element, which detects thecurrent passed through the inductor and the control circuit that turnsoff the switching element when the voltage drop reaches thepreviously-set threshold. Accordingly, the LED lighting device providedwith the easy-to-integrate and easy-to-miniaturize chopper having thesimple circuit configuration can be provided.

The inductor and the driving winding are formed into the planar coilstructure, and at least the switching element and the diode constitutethe integrated circuit that is stacked on at least one surface of theplanar coil structure. Therefore, the distance between the driving coiland the switching element becomes the shortest, and the generation ofthe unnecessary and harmful parasitic inductance or parasiticcapacitance, which causes the noise generation, can be suppressed to theminimum level to improve the stability and reliability of the chopperoperation.

When the switching element, the constant-current unit, and the diode areformed into the integrated circuit comprising the five externalterminals, the high-speed switching is easily performed while the wholeof the chopper is further miniaturized.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A lighting device comprising: an input end; achopper including: a switching element electrically connected to theinput end, the switching element having a control terminal, a currentcontrol unit electrically connected to the switching element, aninductor, a first current being passed in the inductor at least when theswitching element is in an on state, a diode, a second current beingpassed in the diode at least when the switching element is in an offstate, and a driving winding magnetically coupled to the inductor andelectrically connected to the control terminal of the switching element;and an output end electrically connected to the chopper and asemiconductor light emitting element.
 2. The device according to claim1, wherein at least one of the switching element, the current controlunit, and the diode includes gallium nitride.
 3. The device according toclaim 1, wherein the inductor and the driving winding are formed by aplanar coil structure.
 4. The device according to claim 1, wherein: theswitching element has a connection point electrically connected to thecurrent control unit, and the switching element is turned off when acurrent in the current control unit reaches a predetermined value, andwhen an electric potential of the connection point is higher than anelectric potential of the control terminal.
 5. The device according toclaim 1, wherein the current control unit includes one of aconstant-current diode, a junction type FET, a three terminal regulator,a GaN-HEMT and a current mirror circuit.
 6. An illuminating apparatuscomprising: a lighting device according to claim 1; and a semiconductorlight emitting element electrically connected to the output end.
 7. Anintegrated circuit comprising: a switching element having a controlterminal and a pair of main terminals; a current control unit having acontrol terminal and a pair of main terminals; and a diode having a pairof main terminals, wherein: the switching element, the current controlunit, and the diode constitute a series connection body such that eachof the main terminals are electrically connected in series, the seriesconnection body has one end and another end, the one end being one ofthe main terminals, the one of the main terminals being not connected toevery other of the main terminals, the other end being another of themain terminals, the other of the main terminals being not connected toevery other of the main terminals, and the series connection bodyincludes: a first external terminal electrically connected to the oneend, a second external terminal electrically connected to the other end,a third external terminal being led out from a connection point suchthat two of the main terminals are connected to each other, a fourthexternal terminal being led out from the control terminal of theswitching element, and a fifth external terminal being led out from thecontrol terminal of the current control unit.
 8. The circuit accordingto claim 7, wherein at least one of the switching element, the currentcontrol unit, and the diode includes gallium nitride.
 9. The circuitaccording to claim 7, wherein: the switching element is a normally-ontype field effect transistor, the switching element has a source and adrain as the pair of main terminals, and the switching element has agate as the control terminal.
 10. The circuit according to claim 7,wherein: the current control unit is a normally-on type field effecttransistor, the current control unit has a source and a drain as thepair of main terminals, and the current control unit has a gate as thecontrol terminal.
 11. A power-supply device comprising: an integratedcircuit according to claim 7; an inductor electrically connected to thethird external terminal; and a driving winding magnetically coupled tothe inductor and electrically connected to the fourth external terminal.12. An illuminating apparatus comprising: a power-supply deviceaccording to claim 11; and a semiconductor light emitting element, thepower-supply device supplying a power to the semiconductor lightemitting element.